Despite recent advances in genomic sequencing efforts, as well as in the fields of pre-clinical drug screening/development and clinical trial design, the transfer of existing xe2x80x9cpre-clinicalxe2x80x9d knowledge into the clinic is still very difficult. This is mainly due to the sparse knowledge of the events that occur during the initiation, the perpetuation and the maintenance of inflammatory disease states in humans.
The reasons for such incomplete and often low quality information are numerous: humans cannot intentionally be studied in the pre-clinical phase, cell isolation is difficult from human tissue, the starting events of an autoimmune reaction occur without notice, and patients with autoimmune or other inflammatory diseases may not wish to be treated as experimental subjects. As a result, there is a lack of reliable information on which to base decisions about clinical trials. When clinical symptoms arise and treatment is required, rational selection from among the many potential anti-inflammatory compounds or combinations thereof is difficult.
In order to identify new and useful drugs, screening assays must be able to provide biologically relevant information, so that there is a good correlation between the information generated by the screening assay and the pharmaceutical effectiveness of the compound. Some of the more important features for pharmaceutical effectiveness are specificity for the targeted cell or disease, a lack of toxicity at relevant dosages, and specific activity of the compound against its molecular or cellular target.
Inflammatory conditions, particularly chronic inflammatory diseases, are of particular interest. These diseases are caused by the action of the immune system, including the inappropriate activation of T cells, expression of regulatory cytokines and chemokines, loss of immune tolerance, and the like. Modulation of the immune response varies with the specific factors produced, and the receptors present on the responding cell.
Among these diseases are autoimmune and/or chronic inflammatory diseases, which include multiple sclerosis and inflammatory bowel diseases (IBD, ulcerative colitis and Crohn""s disease), colitis , diseases of the joints, such as rheumatoid arthritis, attacks on nucleic acids, as observed with systemic lupus erythematosus and such other diseases as psoriasis, insulin dependent diabetes mellitus (IDDM), Sjogren""s disease, myasthenia gravis, thyroid disease, Alzheimer disease, uveitis, and cardiovascular diseases.
The initiating step in autoimmune disease pathology is still mysterious in many cases, particularly in humans where the diseases are largely sporadic, and symptoms may appear years after the first T cell launches its attack. It has therefore been difficult to design effective therapies that prevent initiation of disease, although there are common features in many of the later stages of disease. Inflammation at the site of the disease is often found, caused by the release of inflammatory cytokines by T cells and other pro-inflammatory cells (e.g. macrophages, dendritic cells, B cells, NK cells), and accompanied by the destruction of autologous cells.
Recent studies using murine models of experimental chronic inflammation are defining the nature of the immunological disturbances that initiate inflammation and destruction of specific organs (for example, see Mombaerts et al. Cell, 1993. 75(2): p. 274-82; Tarrant et al. J Immunol, 1998. 161(1): p. 122-7; Powrie et al. Immunity, 1994. 1: p. 553-562; Hong et al. J Immunol, 1999. 162(12): p. 7480-91; Horak, Clin Immunol Immunopathol, 1995. 76(3 Pt 2): p. S172-3; Ehrhardt et al. J Immunol, 1997. 158(2): p. 566-73; Davidson et al., J Immunol, 1998. 161(6): p. 3143-9; Kuhn et al. Cell, 1993. 75(2): p. 263-74; Neurath et al., J Exp Med, 1995. 182(5): p. 1281-90). Increased understanding of disease promoting inflammatory cells is providing insights into the mechanism controlling the immune responses within target organs.
Evidence has been presented in the literature for the involvement of different T cell subsets in the development of disease. An important role for a distinct T cell population including regulatory and/or suppressor T cells in maintaining the physical integrity of organ specific immunity has been suggested by recent several studies (Suri-Payer et al., J Immunol, 1998. 160(3): p. 1212-8; Shevach et al., Novartis Found Symp, 1998. 215: p. 200-11). These investigators and others (Shimizu et al., J Immunol, 1999. 163(10): p. 5211-8; Itoh et al., J Immunol, 1999. 162(9): p. 5317-26; Sakaguchi et al J Immunol, 1995. 155(3): p. 1151-64; Takahashi et al., Int Immunol, 1998. 10(12): p. 1969-80) have postulated that CD4+ CD25+ T cells play a crucial role in the suppression of immune responses and one might postulate if a cell population is transferred into an immunodeficient mouse without its suppressor CD25+ subset, autoimmunity can occur at multiple sites of the body. This presumes of course that autoimmune causing effector cells are able to reach their target organ. Such an effector cell permissive environment is probably created through the upregulation of adhesion molecules (Berg et al., Immunol Rev, 1989. 108: p. 5-18; von Andrian et al., Proc Natl Acad Sci USA, 1991. 88(17): p. 7538-42; Berg et al., J Exp Med, 1991. 174(6): p. 1461-6; Picker et al. J Immunol, 1990. 145(10): p. 3247-55) and the secretion of chemokines (Baggiolini, Nature, 1998. 392(6676): p. 565-8) on the affected tissues, and on endothelial cells allowing the entrance and retention of effector cells into the tissue.
To study the regulatory effects of T cells and other immunocompetent cells, animal models have provided a very good tool in the past. An essential role for the study of human autoimmune conditions was played in particular by the scid/scid CD4+CD45Rbhi cell transfer model. Over the last decade this model has proven to be a viable scientific tool for the study of dysregulated immune responses, and moreover, has been proven to be a good tool for the discovery and evaluation of treatment/drug targets, candidates for inflammatory bowel disease and recently psoriasis (Hong et al., supra.; Powrie et al., J Exp Med, 1996. 183(6): p. 2669-74; Schon et al., Nat Med, 1997. 3(2): p. 183-8). Notably, not only do these animal models resemble human histology and physiology in some ways or another, but have been helpful in determining novel treatment strategies in humans for both diseases.
One major disadvantage of conventional animal models is that they are very labor-intensive and costly and thus do not permit large throughput drug screening. Unfortunately, in vitro screening techniques are limited in their predictive power. Thus, despite today""s advances in pre-clinical science, hard decisions must be made without complete pre-clinical, in vivo data.
With drug discovery moving from target identification to validations, reliable biological systems are necessary to confirm, validate and support the recent explosion in the number of potential new drug targets and drug compounds. The development of robust, reproducible and scaleable animal models that physiologically resemble human disease is very desirable; i.e. models in which the inflammation is truly chronic in nature and the histology that of human, and can be used as treatment models and not only preventive ones. Such animal models must posses the utility to rapidly advance experimental drug leads rapidly and reliably in a semi- to high through-put fashion, leading to novel, effective and safe therapeutics.
Models are provided for chronic inflammatory diseases. The models are useful for testing and screening of biologically active agents for the treatment of chronic and acute inflammatory disease. A cell population comprising immunocompetent effector cells, which lacks CD25+ suppressor T cells, is transferred into a cellular environment that lacks CD25+ suppressor T cells but contains a T cell antigen. Preferably, an immunostimulant and/or immunomodulatory co-factor and/or T cell antigen is introduced at a targeted site or organ after the T cell introduction to enhance T cell response and homing. Animals develop acute and chronic inflammatory responses at the targeted site, and provide a useful model for the development of inflammation, and for drug/gene screening in the prevention and treatment of chronic inflammatory disease in humans.